Throttle valve control apparatus using DC torque motor

ABSTRACT

A throttle valve control apparatus includes a throttle valve, a DC torque motor for driving the throttle valve, the DC torque motor including a stator with coil wound therearound, and a needle including permanent magnets, the needle being rocked within a predetermined working angle range, wherein a magnetic path is formed within the stator, and a magnetic flux quantity is generated within the stator when current flows in the permanent magnets and the coil, wherein a magnetic flux is not saturated while the working angle of the needle is in a repulsion region where the needle repulses the stator and the magnetic flux is saturated while the working angle of the needle is in an attraction region where the needle is attracted to the stator, a throttle opening sensor for outputting information regarding an opening of the throttle valve, and a controller which controls the dc torque motor when receiving signals from the throttle opening sensor.

This application is a division of application Ser. No. 09/307,795, filedon May 10, 1999, now U.S. Pat. No. 6,153,952.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a small-sized, light-weight DC torquemotor which has good response characteristics and is simple to control,a drive control apparatus using the DC torque motor and a throttle valvecontrol apparatus for an internal combustion engine.

2. Description of the Related Art

Conventionally, there has known a torque motor being rocked within apredetermined working angle range. For example, as shown in FIG. 11,Japanese Unexamined Patent Publication 6-6964 discloses a DC torquemotor 100 consisting of a needle 101 rockable around axis 103 and agenerally U-shaped stator 102 with a cavity disposed between them,wherein the needle 101 is composed of a soft iron core 104 and twopermanent magnets 105, 106 fixedly attached to the periphery of the core104, and the stator 102 has polarity portions 109, 110 facing to eachother and coil 112 is wound around the proximal portion of the stator102 (the upper part in FIG. 11).

In the above-specified DC torque motor and the like, torque is designedto be almost constant irrespectively of degree of angle within apredetermined angle range on condition that the current flowing in thecoil is set constant. That is, the torque is designed to be flat to anyangles within the predetermined angle range. For example, theabove-mentioned publication discloses a DC torque motor capable ofsecuring constant torque with constant flowing of current at almostentire ratable positions for the needle.

However, section area of the stator 102 (section area of magnetic path)needs to be large so as to achieve such characteristics. The stator 102is affected by magnetic fields of the permanent magnets 105, 106 fixedlyattached to the needle 101 and a magnetic field generated by currentflowing in the coil 112. However, directions of the above-statedmagnetic fields may sometimes coincide with each other, which depends onangle a of the needle 101. Under such a condition, since the stator 102is made of soft magnetic material such as soft iron, once fluxoidquantum is saturated, the fluxoid quantum does not increase greatly evenwhen current flows in the coil. As a result, torque becomes low inproportion to a variation of the fluxoid quantum. Therefore, sectionarea of magnetic path needs to be made large to avoid saturation of thefluxoid quantum.

However, as the section area of magnetic path for the stator 102 isenlarged, dimensions, volume, weight of the stator 102 increaseproportionally. Further, in case that a DC torque motor is controlled byangle of its shaft (rocking angle) α, large torque is required at theinitial rocking so that the DC torque motor can be rocked within a largeangle range to obtain high response characteristics. However, largetorque is not required at the near-to-end rocking. Further, considerablyhigh torque is not required for the DC torque motor to be rocked by asmall angle.

SUMMARY OF THE INVENTION

The present invention has been made in light of the above problems.Therefore, an object of the present invention is to provide asmall-sized, light-weight DC torque motor with good responsibilitycharacteristics, a drive control apparatus using the same and a throttlevalve control apparatus for use in, for example, an internal combustionengine.

To obtain the above-stated object, a moving magnet type DC torque motorrocked in a predetermined working angle range according to the presentinvention, is preferably characterized in that, while it is assumed thatcurrent, angle and torque satisfy the following relationship that: ifcurrent in positive direction is applied, the direction of angle atwhich the DC torque motor is rocked is positive and the direction oftorque developed at this moment is positive; and if current in negativedirection is applied, the direction of angle at which the DC torquemotor is rocked is negative and the direction of torque developed atthis moment is negative; wherein the motor has following angle-torquecharacteristics that positions of torque peaks among the torque inpositive direction developed by the constant current in the positivedirection spread in a low angle region among the working angle range,and positions of torque peaks among the torque in negative directiondeveloped by the constant current in the negative direction spread in ahigh angle region among the working angle range.

The DC torque motor having the above-stated structure according to thepresent invention (to be simply referred to as ‘motor’ hereinafter) hasthe following angle-torque characteristics if the directions of thecurrent, angle and torque are set as described above.

First, a case where the motor is rocked in (positive) direction in whichangle increases is considered. In this case, if the motor is rockedgreatly, that is, if the motor is rocked from a low angle θ1 to a highangle θ2 (θ1<<θ2) as in a case where the motor is rocked from the lowerlimit of the working angle range to the upper limit thereof, positionsof torque peaks unevenly spread in the low angle region. Due to this, ata low angle, i.e., at the beginning of the motor operation, high torquecan be obtained and the motor can be promptly accelerated. In addition,if angle increases, i.e., the motor is near to a stop position, thetorque thus developed is lower. In other words, although the motor isrocked by high angle (θ2−θ1), the motor can be rocked to a desired angleθ2 promptly and smoothly.

Meanwhile, if the motor is to be rocked to a less degree, an angularvariation is small and response speed is not so influential.Accordingly, high torque is not required. Therefore, if the motor is tobe rocked from a high angle θ3 to a slightly higher angle θ4 (θ3<θ4),torque peaks unevenly spread in the low angle region, which does not,however, adversely affect control operation.

Next, a case opposite to the above case, i.e., a case where the motor isto be rocked in (negative) direction at which angle decreases.

In this case, if the motor is rocked to a large degree, i.e., if themotor is rocked from a high angle θ5 to a low angle θ6 (θ5>>θ6) as in acase where the motor is rocked from the upper limit of the working anglerange to the lower limit thereof, torque peaks unevenly spread in a highangle region. Due to this, at high angle θ, that is, at the beginning ofmotor operation, high torque can be obtained and the motor can be,thereby, accelerated promptly. Also, if angle decreases, that is, if themotor is near the stop position, the torque thus developed is lower. Inother words, although the motor is rocked by high angle (θ5−θ6), themotor can be rocked to a desired angle θ6 promptly and smoothly.

Meanwhile, if the motor is to be rocked to a less degree, high torque isnot required and an angular variation is small. Accordingly, responsespeed is not so influential. Due to this, if the motor is to be rockedfrom a low angle θ7 to a slightly lower angle θ8 (θ7>θ8), positions oftorque peaks unevenly spread in the high angle region, which does not,however, adversely affect control operation.

In other words, if angle is to be changed greatly, high torquesufficient to accelerate the motor can be developed and good responsecharacteristics can be obtained. If angle is changed less greatly,torque developed may be low. The low torque does not, however, adverselyaffect control operation.

To obtain the above-stated object, in the inventive DC torque motorcomprising a stator with coil wound therearound, and a needle includingpermanent magnets, the needle being rocked within a predeterminedworking angle range, it is preferable that magnetic path is formedwithin the stator, fluxoid quantum the permanent magnets and currentflowing in the coil generate within the stator is not saturated whilethe working angle of the needle is in a repulsion region where theneedle repulses the stator, and saturated while the working angle of theneedle is in an attraction region where the needle is attracted to thestator.

Furthermore, in the DC torque motor according to the present invention,it is preferably that a magnetic flux quantity acquired by product ofminimum section area of the stator and saturation magnetic flux densityof the stator is smaller than a fluxoid quantum acquired by sum ofmaximum magnetic flux quantity the current flowing in the coil generatesand maximum permanent fluxoid quantum the permanent magnets generatewithin the working angle range.

Still further, in the DC torque motor according to the presentinvention, it is preferable that the stator is composed of magneticsteel sheets superimposed, whose saturation magnetic flux density islarger than 1.6 T (tesla).

In the DC torque motor, torque T developed in the motor at a certainangle is proportional to a variation Δφ(=φ−φ0of fluxoid quantum from φ0to φ by adding a magnetic field Hc generated within the stator byapplying current to the coil to a magnetic field H0 generated within thestator by the magnets (T ∝Δφ). Also, in the DC torque motor, the workingangle range is divided into a repulsion region in which torque is mainlydeveloped by a repulsion force between the magnets and the magneticpoles in the stator, and an attraction region, opposite to the repulsionregion, in which torque is mainly developed by an attraction forcebetween the magnets and the magnetic poles in the stator. That is, therepulsion region herein means a rotating angle region of the needlewhere the needle including magnets is affected by repulsion force of thestator more greatly than attraction force thereof. On the other hand,the attraction region means a rotating angle region of the needle wherethe needle is affected by attraction force of the stator more greatlythan repulsion force thereof.

Further, in the DC torque motor, if the motor is rocked (or rotated) in(positive) direction in which angle increases, the motor is operatedsuch that a low angle region is in the repulsion region and a high angleregion is in the attraction region. In other words, coil current isapplied to obtain such directions. Conversely, if the motor is rocked in(negative) direction in which angle decreases, the motor is operatedsuch that a high angle region is in the repulsion region and a low angleregion is in the attraction region. In other words, if the motor isrocked by high angle such as rocked from one end of the working anglerange to the other end thereof, the repulsion region is always employedat the beginning of rocking operation.

In the DC torque motor having the above-stated structure according tothe present invention, the magnetic path of the stator has the sectionarea as stated above. If the needle is in the repulsion region, themagnetic field H0 generated by the magnets is opposite in direction tothe magnetic field Hc generated by the coil. In this state, magneticflux quantity within the stator is on the decrease and is not saturated.As a result, the variation Δφ of the fluxoid quantum φ increases, sothat high torque can be developed.

Meanwhile, if the needle is in the attraction region, the magnetic fieldH0 generated by the magnets is the same in direction as the magneticfield Hc generated by the coil. In this case, while the magnetic path ofthe stator has a small section area, even if the magnetic field Hc isadded to the magnetic field H0, the magnetic flux quantity φ within thestator does not increase from that φ0 caused by the magnets. This isbecause the magnetic flux quantity φ within the stator is saturated. Asa result, even if the magnetic field H is increased by adding themagnetic field Hc to the field H, the magnetic flux quantity φ does notgreatly increase and the variation Δφ of the magnetic flux quantity φdecreases, so that the resultant torque is low.

Accordingly, in the above-stated motor, if angle greatly varies such as,for example, from the repulsion region to the attraction region, themotor can be sufficiently accelerated with high torque and good responsecharacteristics can be thereby obtained. On the other hand, if anglevaries only within the attraction region, the resultant torque may below. In this case, however, not so high torque is not required and thelow torque does not adversely affect control operation. Besides, thestator has a magnetic path of a small section area enough to saturatefluxoid quantum in the attraction region, the stator of smalldimensions, low volume and light weight may suffice, so that asmall-sized, light-weight DC torque motor can be provided.

In these types of DC torque motors, it is preferable that theangle-torque characteristics in a case a low current is applied has afeature in that the characteristics is substantially constant in theworking angle range irrespectively of the degree of angle. For instance,maximum coil current or a low current of about 20% of rated current isto be applied to the DC torque motor, it is considered that high torqueis not inherently required. In these cases, only if the torque hasalmost constant characteristics irrespective of the degree of angle,adjustments, such as changing coefficients for feedback control inaccordance with angle, need not be made or the adjustments can be easilymade. Thereby, control algorithm is simplified and operation istherefore, simplified.

Furthermore, a drive control apparatus using a DC torque motor accordingto the present invention is preferably provided with the above-stated DCtorque motor and conducts feedback control to the DC torque motor basedon the above-stated angle.

The drive control apparatus having the above structure according to thepresent invention conducts feedback control based on the angle by usingthe DC torque motor having the above-stated angle-torquecharacteristics. Due to this, if the angle of the rocking shaft is to bechanged greatly, the motor is accelerated with high torque, therebyallowing angular control with good response characteristics. Meanwhile,even if the angle of the rocking shaft is to be changed to a lessdegree, stable angular control can be realized without causing anyproblems. That is to say, stable control with good responsecharacteristics can be realized.

The angular feedback control includes not only feedback control bydirectly measuring the angle of the rocking shaft but also indirectcontrol of the angle by measuring physical quantity corresponding to theangle such as the opening of the valve and by using the resultantphysical quantity. PD control and PID control based on the deviation ofa present angle from a desired angle can be used as the feedback controlmethod. Robust control, H ∝ control and other control methods may alsobe applied in consideration of the control accuracy and the like of thedrive control apparatus.

The drive control apparatus includes, for example, a drive controlapparatus for controlling the opening/closing of the throttle valve inan internal combustion engine. In addition, a valve drive controlapparatus for controlling the opening/closing of various valves, arocking shaft angle control apparatus in various machines andapparatuses and the like may be applied.

Moreover, to obtain the above-stated object, a throttle valve controlapparatus according to the present invention preferably includes athrottle valve, a DC torque motor for opening/closing the throttle asstated forgoing, and a throttle opening sensor for outputtinginformation on the opening of the throttle valve.

The throttle valve control apparatus having the above-stated structureaccording to the present invention opens/closes the throttle valve usingthe DC torque motor having the above-stated angle-torque characteristicsand includes the throttle opening sensor Due to this, if the opening ofthe throttle valve is greatly changed (for example, from a fully closedstate to a fully opened state), the rocking of the throttle valve can beaccelerated with high torque at the beginning of the rocking operationand good response characteristics can be, thereby, obtained byconducting feedback control using the output of this throttle openingsensor. If the opening of the throttle valve is changed to a lessdegree, on the other hand, the torque developed may be low, which lowtorque does not, however, adversely affect control operation. Thus, itis possible to easily and stably control the throttle valve to havedesired opening. Besides, the DC torque motor can be made small andlight-weight and a small-sized, light-weight throttle valve controlapparatus can be, therefore, obtained.

Any throttle opening sensors may suffice as long as they can detectopening. For instance, a sensor consisting of a potentiometer and arotary encoder may be used.

Preferably, the above-stated throttle valve control apparatus furtherincludes a back spring urging the throttle valve toward valve closingdirection wherein holding coil current applied to the above-stated DCtorque motor is substantially constant in the working angle rangeirrespectively of the degree of angle so as to obtain holding torque forholding the opening of the throttle valve while matching torquedeveloped by the back spring torque.

For example, in the DC torque motor according to the present invention,holding current for holding the throttle valve at the present positionis constantly at of about 1A irrespectively of working angle of thethrottle valve when maximum current value of the DC torque motor is 5A.

Some throttle valve control apparatus includes a back spring for urgingthe throttle valve toward valve closing direction so as to automaticallyclose the throttle valve when the motor malfunctions and the like. Thisback spring is set to have a small spring constant and, therefore,torque developed by the back spring is set not to increase greatly evenif the opening of the valve increases. In the throttle valve controlapparatus of this type, coil current (or holding coil current) forgenerating holding torque which matches the torque caused by urging thevalve by the back spring, is applied to the motor.

In that case, if the holding coil current is substantially constant inthe working angle range irrespectively of the degree of angle orsubstantially constant in a range from the fully closed state to thefully opened states of the throttle valve irrespectively of the openingof the throttle valve, adjustments, such as changing coefficients forfeedback control in accordance with the opening are not required or canbe easily made while feedback controlling the opening of the throttlevalve. Thus, control algorithm is simplified and feedback control isthereby simplified.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) arc explanatory views showing configuration of a DCtorque motor according to the First embodiment;

FIG 2 is a graph showing angle-torque characteristics of a DC torquemotor according to the First embodiment;

FIG. 3 is a graph showing relationship between magnetic field generatedin a stator and fluxoid quantum obtained when current is not applied tocoil, which is to explain the reason why such angle-torquecharacteristics occurs to a DC que motor according to the Firstembodiment;

FIG. 4 is a graph showing relationship between magnetic field andfluxoid quantum generated in a stator on condition that current isapplied to coil according to the graph of FIG. 3;

FIG. 5 is a graph showing relationship between exciting current andgenerated magnetic flux;

FIG. 6(a) shows a schematic view of a DC torque motor according toComparison Example wherein section area of magnetic path in a stator ismade larger than that of a motor according to the First Embodiment;

FIG. 6(b) is a graph showing angle-torque characteristics of a DC torquemotor according to Comparison Example;

FIG. 7 is a diagram to illustrate a drive control apparatus for drivingmachine according to the Second Embodiment using a DC torque motoraccording to the First Embodiment;

FIG. 8 is a diagram to illustrate a throttle valve control apparatus foropening/closing throttle valve of the Third Embodiment using a DC torquemotor according to the First Embodiment;

FIG. 9 is a schematic diagram to illustrate opening of throttle valve inview of relationship between back spring 36 and relief spring 37;

FIG. 10 is a diagram to illustrate control system wherein a throttlevalve control apparatus shown in FIG. 8 is controlled by Engine ControlUnit; and

FIG. 11 is an explanatory view showing configuration of a conventionalDC torque motor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described in detail belowwith reference to the accompanying drawings.

First Embodiment

FIG. 1 is an explanatory view showing the configuration of a DC torquemotor 10 according to the First embodiment. The DC torque motor 10 is asingle-polar moving magnet type DC torque motor. Namely, the motor 10 isof a columnar shape about a shaft 3 and consists of a needle 1 and agenerally U-shaped stator 2 made of soft iron keeping a predeterminedcavity between the needle 1 and the stator 2, wherein the needle 1includes hemicylindrical permanent magnets 5 and 6 fixedly attachedthereto around a core 4 made of soft iron, first and second magneticpole sections 7 and 8 are arranged on the end portions of the stator 2facing to each other, and coil 9 is wound around the proximal portion ofthe stator 2 (the upper portion in FIG. 1). The stator 2 is composed ofmagnetic steel sheets superimposed, whose saturation magnetic fluxdensity is larger than 1.6 T (tesla). FIG. 1(b) shows X—X sectionindicated in FIG. 1(a). Since magnetic steel sheets are superimposed,X—X section of the stator 2 is a rectangular shape. Section area of theX—X section is Acm².

The permanent magnets 5 and 6 fixedly attached to the core 4 aremagnetized in opposite directions. That is, the magnet 5 has a frontsurface (outer peripheral surface) at N pole and a back surface (innersurface) at S pole, whereas the magnet 6 has a front surface (outerperipheral surface) at S pole and a back surface (inner surface) at Npole. The permanent magnets 5 and 6 and a coil current Ic flowing acrossthe coil 9 generate magnetic poles at the first and second magnetic polesections 7 and 8 of the stator 2. The needle 1 repulses from andattracts the resultant magnetic poles and is rocked around the shaft 3by a predetermined range of angles. In the motor 10 according to thisembodiment, the rocking angle θ of the needle 1 (shaft 3) is defined asan angle of line C connecting the boundary between the two magnets 5 and6 and the shaft 3 with respect to a center line B passing the shaft 3and between the first magnetic pole section 7 and the second magneticpole section 8, the angle θ being a positive in an arrow direction inFIG. 1 (clockwise).

Although the motor 10 in this embodiment is, in theory, rockable in arange of θ=0 to 180 degrees, it is stable around θ=0 and 180 degrees atwhich the rocking direction is indeterminate and torque is extremelylowered. Considering this, the range of the rocking angle θ is limitedto 90 degrees, i.e., θ=45 to 135 degrees in this embodiment.

Unlike the above-stated conventional motor 100 (see FIG. 11) and a motor110 (see FIG. 6(a)) according to Comparison Example to be describedlater, it is noted that arms of the stator 2 for the motor 10 is, formedto be slightly thinner than the two magnetic pole sections 7 and 8. As aresult, using the stator 2 as a magnetic path circuit, magnetic fluxquantity passing through the stator 2 is easily saturated in a part ofthe stator 2 having the smallest section area A (X—X section).

Next, FIG. 2 shows the relationship between the angle θ of the motor 10and torque T in this embodiment. In FIG. 2, the magnitude of the torqueT energized when coil current Ic flows is indicated with the coilcurrent Ic used as parameter while the needle 1 (shaft 3) is fixed at acertain angle θ. In this embodiment, the angle θ is taken in thehorizontal axis, torque (rocking torque) T at a time when the motor isrocked in a direction in which the angle θ increases is assumed aspositive torque and that at a time when the motor rocked in a directionin which the angle θ decreases is assumed as negative torque. Also, thedirection of the coil current Ic for energizing the rocking torque T inthe positive direction is assumed as positive direction, whereas thedirection of the coil current Ic for energizing the rocking torque T innegative direction.

Therefore, the motor 10 in this embodiment develops rocking torque T inpositive direction if positive coil current Ic is applied and rockingtorque T in negative direction if negative coil current Ic is applied.

Now, taking note of the angle-torque characteristics of the motor 10 asshown in FIG. 2, it is seen from the respective graphs with respect torelatively high positive coil currents Ic=2A, 3A, 4A and 5A in the motor10 having the highest currents Ic=±5A that the peaks (torque peak) ofrocking torque T at those current Ic=2A, 3A, 4A and 5A are unevenlydistributed in a low angle region of θ (e.g., if Ic=5A, the peak is in arange of about 50 to 80 degrees). From the respective graphs whererelatively high (absolute values of) negative coil currents Ic=−2A, −3A,−4A and −5A, it is seen that the negative peaks (torque peak) of rockingtorque T are unevenly distributed in a high angle range of θ (i.e., ifIc=−5A, the peak torque is in a range of about 95 to 130 degrees).

In case of relatively low coil currents Ic=1A and −1A, almost flattorque characteristics are shown in a working angle range of θ=45 to 135degrees.

The above-mentioned angle-torque characteristics of the motor 10 areconsidered to be due to the following qualitative reasons. Note that noconsideration is given herein to the residual magnetic flux quantity forthe brevity of description.

First, in a state in which no coil current Ic is applied as shown inFIG. 3, the horizontal axis indicates a magnetic field H0 generatedwithin the stator 2 by the magnets 5 and 6 and the vertical axisindicates fluxoid quantum φ in the stator 2. The strength of themagnetic field H0 corresponds to the position of the needle 1, i.e., tothe angle θ and reaches a maximum at angles θ=0 and 180 degrees at whichthe polarities are opposite to each other. When θ=90 degrees, H0=0.While it is assumed that the magnetic fields generated within the stator2 at angles θ=0 to 90 degrees are negative and the direction of themagnetic flux generated in the stator 2 is negative, whereas themagnetic fields generated within the stator 2 at angles θ=90 to 180degrees are positive and the direction of the magnetic flux generated inthe stator 2 is positive.

Then, since the stator 2 is made of soft magnetic material (soft iron),the relationship between the magnetic field H0 and magnetic fluxquantity φ is represented as a curve as shown in FIG. 3. It is notedthat the needle 1 of the motor 10 is in a state as shown in the lowerpart of FIG. 3 at angles 45 and 135 degrees corresponding to themagnetic fields indicated by broken lines. At this moment, within thestator 2, the magnetic field H0 in a direction indicated by solid linesoccurs. In the motor 10 shown in the lower part of FIG. 3, thehemicylindrical magnets 5 and 6 of the needle 1 are schematic to clearlyshow the magnetic poles (N pole, S pole) seen on the surface of theneedle 1. Thus, at the working angle of θ=45 to 135 degrees, thestrength of the magnetic field H0 varies between the two broken lines.

Now, a case where coil current Ic flows across the coil 9 is considered.In this case, a magnetic field is generated also by the coil current Ic.FIG. 4 is the same as the graph shown in FIG. 3, where the horizontalaxis indicates the magnetic field H generated within the stator 2, i.e.,the sum of the magnetic fields of the magnets 5, 6 and the coil 9. Forinstance, if the needle 1 is held at an angle θ=45 degrees as shown inthe lower left of FIG. 4, so as to rock the motor 10 in a (positive)direction at which angle θ increases, it is necessary to apply a coilcurrent Ic in the positive direction, and, as shown in the lower leftpart of FIG. 4, so as to generate a magnetic field H1 opposite indirection to the magnetic field H0 generated by the magnets 5 and 6 tothereby allow the magnetic pole sections of the stator 2 to repulse fromthe magnets 5 and 6. Due to this, the strength of the magnetic field Hwithin the stator 2 is shifted by H1 in the right direction of FIG. 4.That is, the absolute value of the strength of the magnetic field Hwithin the stator 2 is decreased. As a result, magnetic flux quantity φwithin the stator 2 varies by Δφ1 (i.e., the absolute value of magneticflux quantity φ is decreased). That is, in FIG. 4, φ45 indicatesmagnetic flux quantity decreased.

Meanwhile, as shown in the upper right portion of FIG. 4, if the motor10 is rocked in a (positive) direction so that the angle θ increases,i.e., the angle θ is close to the broken line range of θ=135 degrees, acoil current Ic in the same (positive) direction as that when themagnetic field H1 is generated is applied and a magnetic field H2 in thesame direction is generated. In this case, however, as shown in thelower right part of FIG. 4, the magnetic fields H0 generated by themagnets 5 and 6 and H2 are the same in direction and the magnets 5 and 6and the magnetic pole sections 7 and 8 of the stator 2 attract oneanother. Due to this, the strength of the magnetic field H within thestator 2 is shifted by H2 in the right direction of FIG. 4. That is, theabsolute value of the strength of the magnetic field H within the stator2 increases. As a result, magnetic flux quantity φ within the stator 2varies by Δφ2 (i.e., the absolute value of magnetic flux quantity φincreases). That is, in FIG. 4, φ130 indicates magnetic flux quantityincreased.

It is noted that the variation Δφ2 of fluxoid quantum φ in this case issmaller than the variation Δφ1 as stated above (Δφ1>Δφ2).

The FIG. 5 shows the relationship between exciting current for the coiland generated magnetic flux of the motor 10 according to thisembodiment. The horizontal axis indicates exciting current and themaximum value is 5A. The vertical axis indicates magnetic flux. Whenexciting current is set to 5A, the maximum, magnetic flux is 16 KWb.

The maximum magnetic flux of the magnetic field H2 generated within theworking angle range by the magnets 5 and 6 is 22 KWb and saturationmagnetic flux density B for the stator 2 is 1.6 T (tesla). The sectionarea A is determined to satisfy the condition that product of A and B,namely, B*A, is smaller than 38 KWb which is sum of 16 KWb generated bythe maximum exciting current 5A and 22 KWb by the magnets 5 and 6 withinthe working angle range. In the motor 10 according to this embodiment,it is calculated that A=2.37 cm². Thereby, B*A=37.9 KWb is acquired andthis value is slightly smaller than 38 KWb, the sum of magnetic flux bythe maximum exciting current and magnetic flux by the magnets 5 and 6.

In the motor 10 in this embodiment, the section area A for the magneticpath of the stator 2 is not so increased. Due to this, even if thestrength of the magnetic field H increases, the magnetic flux quantity φgenerated is saturated and is thereby not so increased in the lattercase. In the former case, by contrast, the absolute value of thestrength of the magnetic field H decreases, so that the magnetic fluxquantity φ decreases greatly.

The above description is related to a case where the motor 10 is rockedin a (positive) direction in which the angle θ increases. Even if themotor 10 is rocked in a (negative) direction in which the angle θdecreases and the magnetic fields H3 and H4 are generated by the coil 9,variations Δφ3 and Δφ4 in magnetic flux quantity φ satisfy therelationship of Δφ3>Δφ4 as in the case of the above.

As can be seen from the above description, if the motor 10 is rocked inpositive direction, the magnetic field H0 generated by the magnets 5 and6 is negative, i.e., in the left half of the graph in FIG. 4 or theangle θ is between 0 and 90 degrees, then the magnetic field H0 is in arepulsion region in which torque is developed by the repulsion forcebetween the magnets 5 and 6 of the needle 1 and the magnetic polesections 7 and 8 of the stator 2. If the magnetic field H0 generated bythe magnets 5 and 6 is positive, i.e., the angle θ is between 90 and 180degrees, then the magnetic field H0 is in an attraction region in whichtorque is developed by the attraction force between the magnets 5 and 6of the needle 1 and the magnetic pole section 7 and 8 of the stator 2(see FIG. 2).

Conversely, if the motor 10 is rocked in negative direction and themagnetic field H0 generated by the magnets is positive, i.e., themagnetic field H0 is in the right half side of the graph in FIG. 4 orthe angle θ is between 90 and 180 degrees, then the magnetic field is ina repulsion region as indicated by a word in parenthesis. Also, if themagnetic field H0 by the magnets is negative, i.e., the angle θ isbetween 0 and 90 degrees, the magnetic field is in an attraction regionas indicated by a word in parenthesis.

The rocking torque T energized in the DC torque motor is generallyproportional to the variation Δφ of magnetic flux quantity φ (T ∝Δφ).Therefore, as stated above, while Δφ1>Δφ2, even if the same coil currentIc is applied, high torque is obtained in a region in which the angle θis low with the motor rocked in the positive direction and low torque isobtained in a region in which the angle θ is high. Likewise, whileΔφ3>Δφ4, high torque is obtained in a region in which the angle θ ishigh and low torque is obtained in a region in which the angle θ is lowif the motor is rocked in negative direction. They correspond to thefeature of angle-torque characteristics of the motor 10 (see FIG. 2).

In case of employing the motor 10 having the above-statedcharacteristics (see FIG. 2), the following advantages can be obtained.It is assumed that the angle θ is changed greatly, e.g., the angle θ ischanged from θa=45 degrees to θb=135 degrees. In this case, to providegood response characteristics, it is necessary to sufficientlyaccelerate the motor (or to apply high angular acceleration to themotor) at the beginning of rocking operation. As can be seen from thegraph of FIG. 2, the motor 10, if rocked in positive direction, can besufficiently accelerated since high torque is obtained in a region inwhich the angle θ is low, i.e., in a repulsion region. Meanwhile, themotor is easily stopped in a stop position in which the angle θb isclose to 135 degrees, since the torque developed in the position is low.In other words, although the angle θ is changed by 90 degrees from θa=45degrees to θb=135 degrees, the motor has good response characteristicsand can be rocked smoothly.

Meanwhile, if the angle θ is changed to a less degree, an angularvariation is small and, therefore, high angular acceleration need not beapplied to the motor. Thus, in a case where the angle is changed fromθc=125 degrees to θd=135 degrees and the motor is rocked in positivedirection, the torque developed is low in a region in which the angle θis high, i.e. in an attraction region but the motor can be controlledwithout difficulty, as can be seen from the graph of FIG. 2.

In addition, if the motor is rocked in negative direction and theangular variation is large as in the case of the above, then the motorhas good response characteristic and can be rocked smoothly. If theangular variation is small, the motor can be easily controlled.

In the motor 10 in this embodiment, in particular, if coil currents areIc=1A and −1A, the motor has a flat angle-torque characteristics thattorque T is not changed regardless of the angle θ. The application of alow current to the motor originally means that high torque is notrequired. Therefore, peaks of torque need not unevenly exist as seen ina case where higher coil current Ic is applied. Rather, since the torqueT is not changed by the angle θ, adjustments such as changing controlcoefficients in accordance with the angle are not required or suchadjustments can be easily made if the motor 10 is driven by theangle-based feedback control. As a result, easier control can berealized, e.g., the algorithm for feedback control can be simplified.

Comparison Example

As a Comparison Example of the motor 10, FIG. 6(a) shows a motor 110 inwhich section area M2 of magnetic path for a stator 112 is made largerthan that of the motor 10 according to the First Embodiment. In themotor 110, a needle 1 is identical to the one for the motor 10, however,section area M2 of the stator 112 is made larger than section area A ofthe stator 2 for the motor 10 (M2>A). That is, the stator 112 is madethicker (wider) than the stator 2 for the motor 10 and any portions ofthe stator 112 including magnetic pole sections 117 and 118 are madealmost constant in terms of section area.

Furthermore, FIG. 6(b) shows angle-torque characteristics of the motor110 measured by the same manner as the First Embodiment. It is apparentfrom the graphs of FIG. 6(b) that, in the motor 110, rocking torque T isalmost constant at any degrees of angle within the working angle rangeof θ=45 to 135 degrees irrespectively of its positioning at repulsionregion or attraction region. Such angle-torque characteristics areconsidered due to the enlarged section area M2 for the stator 112. Thatis, the section area M2 is too large to make magnetic flux quantity φ tobe saturated in the stator 112 even if magnetic field generated by coilcurrent Ic is applied thereto. Thereby, sufficiently high torque T canbe obtained.

The motor 110 having such characteristics is considered to be acorrespondent of the above-stated conventional motor. However, sincetorque obtained by adding coil current Ic is almost constantirrespectively of degree of angle θ, the characteristics simplifycontrol of the motor. However, as easily conceivable from FIG. 5, in themotor 110, the stator 112 made of soft iron is considerably large indimensions and volume as compared with the motor 10 according to theFirst Embodiment. Along with this, its weight is considerably heavy,too. As apparent from this, a small-sized, light-weight motor can berealized if making the stator 2 small and light, as described in theFirst Embodiment.

Second Embodiment

Next, as an embodiment of a motor 10 organized in a machine, the SecondEmbodiment describes a drive control apparatus 20 employing the motor 10which is to rock a rocking shaft 21 of a machine (an object to bedriven) 22.

In the drive control apparatus 20, the machine 22 and the motor 10 isconnected by the rocking shaft 21. Further, rocking angle of the rockingshaft 21 is detected by, for example, an angle sensor 23 consisting of apotentiometer. First, analog output of the angle sensor 23 is convertedto digital values by an A/D converter 25 in control unit 24. Then, acomputer 26 conducts a predetermined operation in accordance with acontrol method such as PID control, and calculates drive conditionsusing the deviation of the angle from an objective angle which isseparately input. After that, a motor drive circuit 27 controls value ofcoil current Ic to be added to the motor 10 following the resultantdrive condition and thereby, feedback control of the motor 10 isconducted.

If the rocking shaft 21 is rocked to a large degree by the motor 10, therocking shaft 21 is rocked with high torque at the beginning of therocking operation, whereby high angular acceleration can be obtained.For that reason, the response characteristics can be improved. Besides,when the rocking operation is near to end, the energized torque is lowand the machine 22 can be, therefore, stopped smoothly. On the otherhand, if the rocking shaft 21 is rocked to a less degree, the variationof rocking angle is small and the machine needs not have high responsecharacteristics. Due to this, even if the energized torque is low,stable control can be realized without causing problems. As a result,there is provided a drive control apparatus 20 which has high responsecharacteristics and is simple to control. Furthermore, as stated above,since the stator 2 is small in dimensions and light weight, therebymaking it possible to provide a small-sized, light-weight drive controlapparatus 20.

Third Embodiment

Next, description will be given to another embodiment for employing themotor 10 in relation to a throttle valve control apparatus 30 foropening and closing a throttle valve by the motor 10. In the throttlevalve control apparatus 30 shown in FIG. 8, a butterfly valve typethrottle valve 33 is formed at a throttle shaft 31 passing through aninlet tube 32 in the diameter direction. The throttle shaft 31 is rockedby about 90 degrees from a fully closed state to a fully opened state bythe DC torque motor 10. Further, the rocking angle θ, that is, theopening of the throttle shaft 31 is designed to be detected by, forexample, a throttle opening sensor 34 consisting of a potentiometer. Thethrottle shaft 31 is urged in valve closing direction (in the lowerdirection of FIG. 8) by a back spring 36 through a lever 35 which isL-shaped in FIG. 8.

If the power of the motor 10 is turned off or the motor 10 malfunctions,the throttle shaft 31 is shifted toward the valve closing direction (inthe lower direction of FIG. 8). If the shaft 31 approaches a fullyclosed state, the lever 35 abuts on a full close stopper 38 to preventthe throttle shaft 31 from being urged by the back spring 36. In thisstate, the throttle shaft 31 is urged toward valve opening direction (inthe upper direction of FIG. 8) by a relief spring 37 and the throttlevalve 33 is, therefore, held to slightly open compared with a fullyclosed state.

Since the back spring 36 automatically closes the throttle valve 33 whenthe power of the motor 10 is turned off or the motor 10 malfunctions, iturges the throttle valve 33 in valve closing direction. The back spring36 is made of, for example, a helical spring of many turns and set tohave a small spring constant. Due to this, the torque (back torque) Tbin valve closing direction energized by the back spring 36 does notgreatly increase even if the opening of the throttle valve 33 increases.In other words, the back torque Tb is set to be substantially constantirrespectively of the opening of the valve 33. In addition, the reliefspring 37 prevents the throttle valve 33 from being fully closed afterbeing urged by the back spring 36 when the power of the motor 10 isturned off or the motor 10 malfunctions and holds the throttle valve 33to be slightly opened. That is, the relief spring 37 is designed to urgethe throttle shaft 31 in valve opening direction.

In FIG. 8, the throttle valve 33 is opened upward as indicated by anarrow to show the functions of the relief spring 37 and the back spring36. As can be easily understood, however, the throttle valve 33 and thethrottle shaft 31 are actually rocked about the shaft and the backspring 36 and the relief spring 37 urge and twist the throttle shaft 31about the shaft.

FIG. 9 shows a schematic diagram to illustrate opening of throttle valvein view of relationship between the back spring 36 and the relief spring37. Th1 indicates maximum closing torque including torque by the backspring 36 and dispersion caused by friction. Th2 indicates maximumopening torque including torque by the relief spring 37 and dispersioncaused by friction.

The holding torque for the motor 10 is Th1=1.5 Kg·cm at the maximum. Ifthis maximum holding torque is included in a region in which flat torquecharacteristics can be obtained when constant current is applied to theDC torque motor, control with linear current value can generate torquesurpassing holding torque by the back spring 36, whereby linear controlof the throttle valve 33 can be realized. As a result, feedback controlincluding control algorithm and the like is made easier.

In this embodiment, the rocking angle θ of the motor 10 simplycorresponds to that of the throttle shaft 31. In other words, thethrottle shaft 31 is obtained by extending the core 4 (see FIG. 1) ofthe motor 10 in the axial direction (in a direction perpendicular to thesheet of FIG. 1). In this embodiment, therefore, the motor 10 at therocking angle θ=45 degrees is made correspondent to the throttle valve33 in a fully closed state and the motor 10 at the rocking angle θ=135degrees to the throttle valve 33 in a fully opened state. By doing so,the throttle valve 33 is changed from a fully opened state to a fullyclosed state by the rocking angle of 90 degrees. Thus, in the graphsshown in FIGS. 3 and 4, the broken lines indicating the angle θ=45degrees and θ=135 degrees correspond to the fully closed and fullyopened throttle valve 33, as indicated by the words in parentheses,respectively.

Accordingly, the positive direction of the rocking angle θ of the motor10 corresponds to the opening direction (opening side) of the throttlevalve 33, whereas the negative direction of the rocking angle θ thereofcorresponds to the closing direction (closing side) of the valve 33.Also, the side at which the angle θ is low indicates the throttle valve33 in the closed state, whereas the side at which the angle θ is highindicates the throttle valve 33 in an opened stated.

Next, FIG. 10 shows a state in which the throttle valve controlapparatus 30 is connected to and controlled by an engine control unit(to be referred to as ‘ECU’ hereinafter) 41. The overall apparatusserves as a throttle valve control system 40 corresponding to the drivecontrol apparatus 20 in the second embodiment.

In the throttle valve control apparatus 30 having the above structure,the output of the throttle opening sensor 34 is inputted to the ECU 41.In FIG. 9, the back spring 36 and the like are not shown and thethrottle valve control apparatus 30 is shown to be simplified. In theECU 41, the analog output of the throttle opening sensor 34 is convertedto a digitized throttle opening signal Sig1 by an A/D converter 42. Inaddition, the analog output of an accelerator sensor 46 consisting of apotentiometer for detecting the degree of actuating an accelerator (notshown) operated by a driver is converted to a digitized requestedopening signal Sig2 by the second A/D converter 45. Next, using thedeviation of the throttle opening signal Sig1 from the requested openingsignal Sig2 or the like, a computer 43 conducts a predeterminedoperation in accordance with a control method, such as PID control, andcalculates drive conditions. Using the resultant drive conditions, amotor drive circuit 44 controls the value of the coil current Ic at themotor 10, thereby feedback-control is conducted for the throttle valvecontrol apparatus 30 (or motor 10).

The motor 10 has angle-torque characteristics (see FIG. 2) as statedabove. Owing to this, if the shaft 3 or throttle shaft 31 is rocked to alarge degree, the throttle shaft 31 and the throttle valve 33 are rockedwith high torque at the beginning of the rocking operation, whereby highangular acceleration can be obtained. For that reason, if, for instance,the opening of the throttle valve 33 is changed from around a fullyclosed state (θ is near 45 degrees) to around a fully opened state (θ isnear 135 degrees) or changed from around a fully opened state to a fullyclosed state, it is possible to improve the response characteristics ofthe throttle valve 33. Besides, when the rocking operation is near toend, the energized torque is low and the throttle valve 33 can be,therefore, stopped smoothly. On the other hand, if the throttle shaft 31is rocked to a less degree, the variation of the rocking angle θ issmall and the throttle valve 33 needs not have high responsecharacteristics. Due to this, even if the energized torque is low,stable control can be realized without causing any problems.Furthermore, as stated above, since the stator 2 is small in dimensionsand light-weight, a small-sized, light-weight motor 10 can be provided,thereby making it possible to provide a small-sized, light-weightthrottle valve control apparatus 30. As a result, it is possible toprovide a small-sized, light-weight throttle valve control apparatus 30having good response characteristics and capable of stably controlling athrottle valve.

In the meantime, the throttle valve control apparatus 30 in thisembodiment, the throttle shaft 31 is urged toward the valve openingdirection by the back spring 36 in a normal operation state as alreadystated above. Thus, if the throttle valve 33 is to be held to havecertain opening, i.e., the rocking angle θ of the motor 10 is to be heldto a certain angle θh, a holding coil current Ich needs to be applied tothe motor 10 in positive direction to thereby energize holding torque Thin the valve opening direction so as to almost match the back torque Tbcaused by urging the shaft 31 by the back spring 36.

It is noted that the back spring 36 is set to have a small springconstant as stated above, so that back torque Tb increases less greatlyeven if the opening of the throttle valve 33 increases. If the backspring 31 has a large spring constant and the back torque Tb greatlyvaries (increases) as the opening of the throttle valve 33 increases,high torque and, therefore, high coil current are required to rock thethrottle valve 33 to a full opened state against the back torque Tb. Inaddition, since high holding torque Th which matches the high backtorque Tb is developed to hold the valve 33 to the fully opened state,high holding coil current Ich needs to flow. As a result, consumedcurrent (coil current) increases wastefully.

If represented in the graph of FIG. 2 in which angle-torquecharacteristics are shown, the above-stated back torque Tb is indicatedby a solid line. Since the back torque Tb is in the valve openingdirection, it is expressed as negative rocking torque. The holdingtorque Th to be developed by the motor 10 to hold the opening of thethrottle valve 33 while matching the back torque Tb, is positive torquesymmetric with respect to the back torque Tb about the horizontal axisof the graph as indicated by a dashed line.

If observing angle-torque characteristics in case a coil current Ic=1A,torque is almost constant in the working angle θ range between 45 and135 degrees irrespectively of the angle, compared with a case wherepeaks of torque are unevenly seen in the low angle θ range if a coilcurrent Ic is 2A or more. In FIG. 2, the holding torque Th indicated bya dashed line is in a position adjacent to the graph of angle-torquecharacteristics at coil current Ic=1A. Thus, it is clear that theholding coil current Ich to cause the holding torque Th is almostconstant to 1A or less irrespectively of the angle θ. As a result, ifthe motor 10 is feedback-controlled using the output of the throttleopening sensor 34 to hold the opening of the throttle valve 33 to acertain degree, there is no need to make adjustments, such as to changecoefficients for use in the feedback control operation by the computer43, in accordance with the change of the opening, thereby makingfeedback control easier.

The above-stated embodiments are examples and do not limit the presentinvention in any respect. Accordingly, the present invention can bevariously improved and changed within the scope not departing from thesubject matter thereof.

For example, although the working angle range of a motor 10 according toFirst Embodiment is set to θ=45 to 135 degrees, the working angle rangeis not limited to the above-stated setting range. Working angle range ofa torque motor may be properly adjusted in accordance with requiredangle range for the motor. Moreover, although a single-polar type DCtorque motor is shown in the Embodiments, a plural-polar type DC torquemotor may be used.

Furthermore, although the Third Embodiment describes the throttle valvecontrol apparatus 30 for controlling drive of a throttle valve 33, thepresent invention may be applied to drive control apparatus forcontrolling drive of other type of valve, as well as drive controlapparatus for controlling other types of machine.

Still further, although a core 4 and a throttle shaft 31 are used ascommon parts in the throttle valve control apparatus 30 according to theThird Embodiment, these parts may be replaced with different parts sothat rocking of the core 4 can be transmitted by a gear, timing belt andthe like.

What is claimed is:
 1. A throttle valve control apparatus comprising: athrottle valve; a DC torque motor for driving the throttle valve, the DCtorque motor including a stator with a coil wound therearound, and aneedle including permanent magnets, the needle being rocked within apredetermined working angle range, wherein a magnetic path is formedwithin the stator, and a magnetic flux quantity is generated within thestator by the permanent magnets and by the coil when current flows inthe coil, wherein the sum of the magnetic flux quantities caused by thepermanent magnets and the coil is not saturated while a working angle ofthe needle is in a repulsion region where the needle repulses the statorand magnetic flux is saturated while the working angle of the needle isin an attraction region where the needle is attracted to the stator;throttle opening sensor for outputting information regarding an openingof the throttle valve; and a controller which controls the DC torquemotor when receiving signals from the throttle opening sensor.
 2. Athrottle valve control apparatus according to claim 1 further comprisinga back spring for urging the throttle valve toward a valve closingdirection, wherein a holding-coil-current applied to the DC torque motoris substantially constant in the working angle range irrespective of thedegree of angle so as to obtain holding torque for holding the openingof the throttle valve while matching torque developed by the back springtorque.
 3. A throttle valve control apparatus according to claim 1,wherein a maximum torque value that the back spring generates within theworking angle range is included in a region of the working angle rangewhere approximately flat torque characteristics are obtained when aconstant current is applied to the DC torque motor.
 4. A throttle valvecontrol apparatus according to claim 1, wherein while it is assumed thata current, an angle and a torque satisfy the following relationshipthat: if the current in a positive direction is applied, the directionof said angle at which the DC torque motor is rocked is positive and thedirection of torque developed at this moment is positive: and if currentin negative direction is applied, the direction of angle at which the DCtorque motor is rocked is negative and the direction of torque developedat this moment is negative, the motor has angle-torque characteristicsposition of torque peaks among the torque in a positive directiondeveloped by the constant current in the positive direction spread in alow angle region among the working angle range; and positions of torquepeaks among the torque in a negative direction developed by the constantcurrent in the negative direction spread in a high angle region amongthe working angle range.
 5. A throttle valve control apparatus accordingto claim 1, wherein the DC torque motor comprises: a stator having agenerally U-shape and having arms with end portions facing each otherand having magnetic pole sections arranged thereon; a needle surroundedby the end portions of the stator, being rotatably supported; wherein aportion of the arms of the stator has a section area A smaller than thatof the magnetic pole sections, the stator is formed of a material havinga saturation magnetic flux density B, and the section area A satisfiesthe condition that the product of A and B is smaller than the sum of (i)a magnetic flux quantity which occurs when an electric current flows inthe coil and (ii) a maximum permanent magnetic flux quantity generatedby the permanent magnets within the working angle range.
 6. A throttlevalve control apparatus according to claim 5, wherein the stator of theDC torque motor is composed of magnetic steel sheets superimposed, whosesaturation magnetic flux density is larger than 1.6 T (tesla).